Magnetic recording medium comprising a polyurethane resin coating residual groups derived from specified phosphorous containing compounds

ABSTRACT

A magnetic coating formulation is composed principally of magnetic particles and a binder. At least a portion of the binder is a polyurethane resin synthesized from a reactant mixture of specific phosphorus compound, epoxy compound, isocyanate compound and polyfunctional hydroxy compounds. The reactant mixture may optionally contain a chain extender. The polyurethane resin contains one phosphoric acid group or one residual group derived from phosphoric acid per 3,000-200,000 number average molecular weight of the polyurethane resin, and has a number average molecular weight of 4,000-150,000. A magnetic recording medium with a magnetic coating layer formed from the magnetic coating formulation is also disclosed. The magnetic coating layer features not only excellent dispersion of magnetic particles, in other words, excellent magnetic characteristics but also superb durability.

This is a division of parent application Ser. No. 07/426,132 filed onOct. 24, 1989, U.S. Pat. No. 5,037,934.

The present invention relates to magnetic coating formulations, and fromanother viewpoint to magnetic recording media with a magnetic layerformed principally of magnetic particles and a binder. Magneticrecording media can include, for example, magnetic tapes, magneticdisks, magnetic cards and the like.

In general, a magnetic recording medium carries a magnetic layer whichhas been formed by coating a base film such as a polyester film with amagnetic coating formulation containing magnetic particles and a binderand then drying the thus-coated formulation.

Binders with various resins incorporated therein have conventionallybeen used as binders for magnetic recording media. Among these, usefulare polyurethane resins, vinyl chloride-vinyl acetate copolymer resins,nitrocellulose and the like. However, these binders do not havesufficient dispersing capacity so that they rely in dispersing capacityupon a dispersant such as soybean lecithin or a phosphoric acidcompound. A system formed of a binder and a dispersant blended thereinhowever tends to develop deleterious effects, such as bleeding, on thedurability of the magnetic layer when used for a long time.

To improve the problems referred to above, binders having highdispersing capacity have been proposed, in which hydrophilic polargroups such as hydroxyl groups, carboxyl groups, phosphoric acid groups,sulfonic acid groups or the like have been introduced to improve theaffinity to magnetic particles (Japanese Patent Applications Laid-OpenNos. 92422/1982, 30235/1984, 154633/1984, 15473/1985, 20315/1985 and1110/1987).

With the current technical standard in view, there is an outstandingdemand for the development of a magnetic recording medium excellent notonly in the dispersion of magnetic particles but also in the durabilityof the magnetic layer.

No one has however succeeded yet to provide a magnetic recording mediumwhich can satisfy both requirements for magnetic recording media,namely, high dispersion of magnetic particles and at the same time highabrasion resistance (i.e., durability) of the magnetic layer. Further,no magnetic coating formulation useful for the production of suchmagnetic recording media has been provided yet.

It is an object of the present invention to solve the above problems.

The present inventors have found that a magnetic recording mediumexcellent in the dispersion of magnetic particles can be obtainedwithout impairing the mechanical characteristics of a polyurethane resinwhen a phosphoric-acid-modified polyurethane resin synthesized by addinga bifunctional isocyanate compound and/or a trifunctional isocyanatecompound and a polyfunctional hydroxy compound having a number averagemolecular weight of 400-5,000 and if desired, a chain extender to aphosphoric-acid-modified polyol -- which has been obtained by adding aparticular compound containing a phosphoric acid group to an epoxycompound containing at least two epoxy groups and/or an epoxy compoundcontaining one epoxy group and at least one hydroxyl group -- and thenconducting a urethanation reaction is used as a binder upon productionof the magnetic recording medium, leading to the completion of thepresent invention.

In addition, the present inventors have also found that use of aphosphoric-acid-modified and epoxy-modified polyurethane resin, whichhas been synthesized by conducting the urethanation reaction in thepresence of an epoxy compound, as a binder results in the provision of amagnetic recording medium having a magnetic layer excellent not only inthe dispersion of magnetic particles but also in abrasion resistance anddurability owing to the high crosslinking degree of the resin. Thisfinding has also led to the completion of this invention.

The present invention therefore provides a magnetic recording mediumwhich comprises a magnetic layer composed principally of magneticparticles and a binder. At least a portion of the binder is apolyurethane resin synthesized from a reactant mixture of components(1), (2), (3) and (4) and/or (5) set out below, containing onephosphoric acid group or one residual group derived from phosphoric acidper 3,000-200,000 number average molecular weight of the polyurethaneresin, and having a number average molecular weight of 4,000-150,000 ora polyurethane resin in which phosphoric acid groups or residual groupsderived from phosphoric acid, said groups being being contained in thepolyurethane resin, have been at least partly neutralized with a base:(1) a phosphorus compound (a) represented by a structural formula setout below or a phosphorus compound (b) represented by a structuralformula set out below: ##STR1## wherein R¹ is a hydrogen atom, a phenylgroup, an alkyl group having 1-40 carbon atoms, or an alkylphenyl grouphaving 1-40 carbon atoms, and n is an integer of 0-30. ##STR2## whereinR² is a phenyl group, an alkyl group having 1-40 carbon atoms, or analkylphenyl group having 1-40 carbon atoms;

(2) an epoxy compound having at least two epoxy groups and/or an epoxycompound having one epoxy group and at least one hydroxyl group;

(3) a bifunctional isocyanate compound and/or a trifunctional isocyanatecompound; and

(4) a polyfunctional hydroxy compound having a number average molecularweight of 400-5,000.

The reactant mixture employed upon synthesis of the binder may furthercomprise a chain extender as component (5).

The present invention has made it possible to provide magnetic recordingmedia having a magnetic coating layer which features not only excellentdispersion of magnetic particles but also superb durability.

The term "residual group derived from phosphoric acid" as used hereinmeans a residual group of a phosphoric acid ester such as a phosphoricacid monoester, phosphoric acid diester or phosphoric acid triester.

Phosphorus Compound

In the present invention, the compound (a) is either the compound (a₁)alone or a mixture of the compound (a₁) and the compound (a2). In themixture, the ratio of the compound (a₁) to the compound (a2) can rangefrom 100:0 to 10:90. Specific examples include "Gafac RE-410", "GafacRE-610", "Gafac RE-210", "Gafac RP-710", "Gafac RD-510Y", "GafacRB-410", "Gafac RS-410", "Gafac RS-610" and "Gafac RB-510", all tradenames and products of Toho Chemical Industry Co., Ltd. and GAFChemicals, as well as monoisodecyl phosphate produced by DaihachiChemical Industry Co., Ltd. As examples of the compound (b), may bementioned phenylphosphonic acid and octylphosphonic acid, both producedby Nissan Chemical Industries, Ltd.

Epoxy Compound

Exemplary epoxy compounds include "Epicoat 828", "Epicoat 834", "Epicoat1001", "Epicoat 1002", "Epicoat 003" and "Epicoat 1004", all trade namesfor bisphenol A-epichlorohydrin epoxy resins produced by Yuka ShellEpoxy Kabushiki Kaisha; "Epicoat 152" and "Epicoat 154", both tradenames for phenolic novolak epoxy resins produced by Yuka Shell EpoxyKabushiki Kaisha, and "Smiepoxy ELPN-180" and "Smiepoxy ESPN-180", bothphenolic novolak epoxy resins produced by Sumitomo Chemical Co., Ltd.;"Smiepoxy ESCN-220L", "Smiepoxy 220F", "Smiepoxy 220HH" and "SmiepoxyESMN-220L", all trade names for cresolic novolak epoxy resins producedby Sumitomo Chemical Co., Ltd., "EOCN-102", "EOCN-103" and "EOCN-104",all trade names for cresolic novolak epoxy resins produced by NipponKayaku Co., Ltd., and "Epicoat 180S", trade name for a cresolic novolakepoxy resin produced by Yuka Shell Epoxy Kabushiki Kaisha; "Epicoat604", trade name for a tetrafunctional epoxy resin of the glycidyl aminetype produced by Yuka Shell Epoxy Kabushiki Kaisha; diethylene glycoldiglycidyl ether; bisphenol S diglycidyl ether; spiroglycol diglycidylether; resorcine diglycidyl ether; diglycidyl adipate; triglycidyltrishydroxyethyl isocyanurate; pentaerythritol polyglycidyl ether;diglycidyl terephthalate; diglycidyl orthophthalate; neopentyl glycoldiglycidyl ether; dibromoneopentyl glycol diglycidyl ether;1,6-hexanediol diglycidyl ether; sorbitol polyglycidyl ether; glyceroldiglycidyl ether; diglycerol diglycidyl ether; glycerol triglycidylether; trimethylolpropane diglycidyl ether; trimethylolpropanetriglycidyl ether; diglycerol triglycidyl ether; vinylcyclohexenedioxide; dicyclopentadiene dioxide; 3,4-epoxy-6-methylcyclohexylmethyl3,4-epoxy-6-methylcyclohexanecarbonate; alicyclic diepoxy adipate;diglycidyl tetrahydrophthalate; diglycidyl hexahydrophthalate;diglycidylparaoxybenzoic acid; trihydroxybiphenyl triglycidyl ether;tetraglycidylbenzophenone; bisresorcinol tetraglycidyl ether; bisphenolhexafluoroacetone diglycidyl ether;1,1-bis[4'-(2,3-epoxypropaxy)phenyl]-cyclohexane;hydroxydicyclopentadiene monoxide;bis(3,4-epoxy-6-methyl-cyclohexylmethyl) adipate; and3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate.

As a monofunctional epoxy compound, may be mentioned glycidol(2,3-epoxy-1-propanol) produced by Nippon Oil & Fats Co., Ltd.

Isocyanate Compound

As the isocyanate compound, the following compounds can be used by wayof example:

2,4-tolylene diisocyanate (may be abbreviated as "TDI"); 2,6-tolylenediisocyanate; p-phenylene diisocyanate; diphenylmethane diisocyanate(may be abbreviated as "MDI"); m-phenylene diisocyanate; hexamethylenediisocyanate; tetramethylene diisocyanate;3,3'-dimethoxy-4,4'-biphenylene diisocyanate; 2,4-naphthalenediisocyanate; 3,3'-dimethyl-4,4-biphenylene diisocyanate;4,4'-diphenylene diisocyanate; 4,4'-diisocyanato diphenyl ether;1,5-naphthalene diisocyanate; p-xylylene diisocyanate; m-xylylenediisocyanate; 1,3-diisocyanato methylcyclohexane; 1,4-diisocyanatomethylcyclohexane; 4,4'-diisocyanato dicyclohexane; 4,4'-diisocyanatodicyclohexylmethane; and isophorone diisocyanate.

If necessary, 2,4,4'-triisocyanato diphenyl, benzene triisocyanate orthe like can also be used in a small amount.

Polyfunctional Hydroxy Compound

A polyester polyol, polyether polyol or the like can be used as thepolyfunctional hydroxy compound, namely, polyol in the presentinvention.

Exemplary polyester polyols include adipate polyols such as polyethyleneadipate polyols, polybutylene adipate polyols, polyethylenepropyleneadipate polyols and cyclohexane dimethanol adipate; terephthalic acidpolyols, e.g., "Vyron RUX" and "Vyron RV-200", both trade names andproduced by Toyobo Co., Ltd.; and polycaprolactone polyols, e.g.,"Placcel 212", "Placcel 220", "Placcel 208" and "Placcel 210", all tradenames and produced by Daicel Chemical Industries, Ltd.

On the other hand, usable exemplary polyether polyols includepolyoxyethylene glycol; polyoxypropylene glycol; polyoxyethylenepolyoxypropylene polyols; and polyoxytetramethylene polyols, e.g., "PTG1000" and "PTG 2000", both trade names and produced by Hodogaya ChemicalCo., Ltd.

Other usable illustrative polyfunctional hydroxy compounds includepolycarbonate polyols, e.g., "Desmophen 2020E" (trade name, product ofBayer AG, W. Germany), and "Carbodiol D-1000" and "CarbodiolD-2000"(trade names, products of Toagosei Chemical Industry Co., Ltd.);polybutadiene polyols, e.g., "G-1000", "G-2000" and "G-3000" (tradenames, products of Nippon Soda Co., Ltd.); 3-methyl-1,5-pentane adipatepolyols, e.g., "PMPA 1000" and "PMPA 2000" (trade names, products ofKuraray Co., Ltd.); polypentadiene polyols; castor oil polyols; andβ-methyl-δ-valerolactone polyols, e.g., "PMVL 1000" and "PMVL 2000"(trade names, products of Kuraray Co., Ltd.).

These polyols can be used either singly or in combination.

Phosphoric-Acid-Modified Polyol

In the present invention, the phosphoric-acid-modified polyol can beobtained by reacting an epoxy compound and the above compound (a) or (b)at 40-120° C., preferably at 60-100° C. in the presence or absence of asolvent.

Preferred solvents include methyl ethyl ketone, methyl isobutyl ketone,toluene, cyclohexanone, tetrahydrofuran, etc. These solvents can be usedeither singly or in combination.

Regarding the charge ratio of the compound (a) or (b) to the epoxycompound, 2:1 molar ratio is preferred for the compound (a) while 1:1molar ratio is preferred for the compound (b). However, the epoxycompound may be charged in excess. Further, the above reaction may beconducted in the presence of a polyfunctional polyol and/or a chainextender.

Chain Extender

Exemplary chain extenders include bifunctional to hexafunctional polyolshaving a molecular weight of 500 or lower as well as diamines andalkanolamines containing one or two terminal primary or secondary aminogroups and having a molecular weight of 500 or lower.

Suitable illustrative chain extenders include the following compounds:

(a) Polyols:

Ethylene glycol, diethylene glycol, propylene glycol, dipropyleneglycol, 1,4-butylene glycol, 1,3-butanediol, 1,6-hexylene glycol,glycerin, trimethylolpropane, 3-methyl-3-hydroxy-1,5-pentanediol,pentaerythritol, sorbitol, 1,4-cyclohexanediol,1,4-cyclohexane-dimethanol, xylylene glycol, neopentyl glycol,3-methyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol,3-methyl-1,3-butanediol.

(b) Diamines:

Diamines such as hydrazine, ethylenediamine, tetramethylenediamine,hexamethylenediamine, and 1,4-cyclo-hexanediamine.

(c) Alkanolamines:

Alkanolamines such as ethanolamine, diethanolamine and triethanolamine.(d) Hydroquinone, pyrogallol, 4,4-isopropylidenediphenol, bisphenol Aand polyols obtained by adding propylene oxide and/or ethylene oxide inan arbitrary order to the above-described polyols, diamines andalkanolamines and having a molecular weight of 500 or lower.

(e) Dihydroxycarboxylic acids such as 2,2-dimethylolpropionic acid andtartaric acid.

Urethanation Reaction

In the presence or absence of a solvent, the bifunctional isocyanatecompound and/or the trifunctional isocyanate compound and thepolyfunctional hydroxy compound having the number average molecularweight of 400-5,000 and if necessary the chain extender are added to thephosphoric-acid-modified polyol. In a manner known per se in the art,they are thereafter subjected to the urethanation reaction by theone-shot process or the prepolymer process, thereby synthesizing thephosphoric-acid-modified polyurethane resin. In the reaction, aurethanation catalyst such as di-n-butyltin dilaurate, tin octylate ortriethylenediamine can also be used.

Further, a phosphoric-acid-modified and epoxy-modified resin having amore highly branched structure and a higher hydroxyl content can beproduced provided that an epoxy compound having at least two epoxygroups and/or an epoxy compound having one epoxy group and at least onehydroxy group is added upon conducting the urethanation reaction.

When the epoxy compound is added, the reaction temperature of theurethanation may be 50-160° C., preferably 70-120° C. in the presence ofa solvent or 70-240° C., preferably 120-220° C. in the absence of asolvent.

In addition, upon production of the phosphoric-acid-modified polyoldescribed above, the epoxy compound can be added in an excess amount toleave a portion of the epoxy compound or epoxy groups unreacted. Thisremaining unreacted portion of the epoxy compound or epoxy groups canthen be used as an epoxy compound upon conducting the urethanationreaction.

The phosphoric-acid-modified and epoxy-modified polyurethane resinsynthesized as described above has a high crosslink density and a highhydroxyl content. Hydroxyl groups in its molecular chain or at itsmolecular terminals react with the polyfunctional low-molecularisocyanate compound during a drying step of a resulting magnetic coatingformulation, thereby making it possible to obtain a magnetic recordingmedium with a magnetic coating layer having a still higher crosslinkdensity and excellent abrasion resistance and durability.

Illustrative reaction solvents include tetrahydrofuran, methyl ethylketone, methyl isobutyl ketone, cyclohexanone, dimethylformamide,toluene and xylene. These solvents can be used either singly or incombination.

Polyurethane Resin

The number average molecular weight of the polyurethane resin in thisinvention can be 4,000-150,000, with 5,000-60,000 being preferred. Ifthis number average molecular weight is too low, it will be difficult todraw out sufficient effects for the improvement of the durability of themagnetic coating layer. On the other hand, unduly high number averagemolecular weights will lead to inconvenience such that the resultingmagnetic coating formulation will have a high viscosity.

Incidentally, phosphoric acid groups or residual groups derived fromphosphoric acid, which are contained in the polyurethane resin useful inthe practice of this invention, may be neutralized with a base either inpart or in toto.

The base may be any organic base or inorganic base insofar as it canneutralize phosphoric acid groups or residual groups derived fromphosphoric acid. Such organic and inorganic bases can be used eithersingly or in combination.

Exemplary inorganic bases include lithium hydroxide, sodium hydroxide,potassium hydroxide and ammonia.

On the other hand, illustrative organic bases include amines andderivatives thereof, such as monomethylamine, dimethylamine,trimethylamine, monoethylamine, diethylamine, triethylamine,tributylamine, trioctylamine, tridecylamine, dimethylethanolamine,monoethanolamine, diethanolamine, triethanolamine, morpholine, pyridine,piperazine, piperidine, aniline, dimethylaniline and picoline; hinderedamines such as dimethylsuccinate-1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidinepolycondensation product; cationic polymers such as polyvinylamine; andquaternary ammonium hydroxide such as dodecyldiethylpropylammoniumhydroxide.

When a polyurethane resin obtained in a neutralized form by using thesebases either singly or in combination is employed as a binder, amodified interaction can be developed between the binder and thesurfaces of magnetic particles. Still better dispersing capacity can beobtained depending on the kind of the magnetic particles.

In the case of a urethane resin of the polyester type, theneutralization of acidic groups makes it possible to preventdeterioration of the resin which would otherwise take place when storedover a long period of time.

Although these polyurethane resins are extremely effective binders bythemselves, they can be used in combination with one or more of variousmaterials conventionally known as binders for magnetic coating layers.Specific examples of binders usable in combination with theaforementioned polyurethane resins include phosphoric-acid-unmodifiedpolyurethane resins, phenoxy resins, cellulose resins, epoxy resins,vinyl chloride-vinyl acetate copolymer resins, vinylidene chlorideresins, polyester resins, polyvinyl butyral resins, and chlorinatedvinyl chloride resins.

In addition, other binders also usable in combination with thepolyurethane resins include polyisocyanate compounds which generallyfunction as crosslinking components. Among these, trifunctionallow-molecular isocyanate compounds are particularly preferred. Asexamples of such isocyanate compounds, may be mentioned "Colonate L"(trade name, product of Nippon Polyurethane Industry Co., Ltd.),"Desmodule L" (trade name, product of Bayer AG), and "Takenate D102"(trade name, product of Takeda Chemical Industries, Ltd.).

As to the content of phosphoric acid groups or residual groups derivedfrom phosphoric acid, which are contained in the polyurethane resin, onephosphoric acid group or one residual group derived from phosphoric acidmust be contained per 3,000-200,000, preferably 5,000-40,000 numberaverage molecular weight of the polyurethane resin. No favorable effectscan be expected for the improvement of the dispersibility of magneticparticles if the content is lower than the lower limit or higher thanthe upper limit.

Production Process of Magnetic Recording Medium

Production of the magnetic recording medium according to the presentinvention can be conducted in a similar manner to either one ofconventional processes. For example, the binder, magnetic particles andif necessary, one or more of various additives are mixed together withan organic solvent to prepare a magnetic coating formulation. A basefilm such as a polyester film is then coated with the magnetic coatingformulation. After drying, a surface treatment such as calender rollingis applied.

As the magnetic particles, γ-Fe₂ O₃, mixed crystals of γY-Fe₂ O₃ and Fe₃O₄, cobalt-doped γ-Fe₂ O₃ and Fe₃ O₄, CrO₂, barium ferrite, pure iron,other ferromagnetic alloy particles (e.g., Fe-Co, Co-Ni, Fe-Co-Ni,Fe-Co-B, Fe-Co-Cr-B, Mn-Bi, Mn-Ali, Fe-Co-V), iron nitride and othersimilar magnetic particles are all usable.

As additives which can be added to the magnetic coating formulation asneeded, a variety of materials conventionally known as additives formagnetic coating formulations can be suitably used, such as lubricants,abrasives, dispersants, antistatic agents and fillers.

Further, exemplary solvents usable for the preparation of the magneticcoating formulation include ketones, e.g., acetone, methyl ethyl ketone,methyl isobutyl ketone and cyclohexanone; alcohols, e.g., methanol,ethanol, propanol and butanol; esters, e.g., methyl acetate, ethylacetate and butyl acetate; glycol ethers, e.g., propylene glycolmonomethyl ether, ethylene glycol monoethyl ether and dioxane; theacetate esters of glycol ethers, e.g., ethylene glycol monoethyl etheracetate and propylene glycol monomethyl ether acetate; aromatichydrocarbons, e.g., benzene, toluene and xylene; aliphatic hydrocarbons,e.g., hexane and heptane; nitropropane; tetrahydrofuran;dimethylacetamide; and dimethylformamide.

The present invention will hereinafter be described specifically by thefollowing examples. It should however be borne in mind that the presentinvention is not limited to the following examples only.

EXAMPLE 1

A 2-l flask equipped with a thermometer, a stirrer, a nitrogen gas inlettube and a reflux condenser was charged with 316 g of phenylphosphonicacid (product of Nissan Chemical Industries, Ltd.) and 316 g of methylethyl ketone, followed by the dropwise addition of a solution of 372 gof "Epicoat 828" (trade name, product of Yuka Shell Epoxy KabushikiKaisha, epoxy equivalent: 186) in the same amount of methyl ethyl ketoneat 70° C. over 30 minutes. They were reacted at 70° C. for 5 hours.

Thereafter, the solvent was driven off by a rotary evaporator to obtaina viscous reaction product having an acid value of 160.

EXAMPLE 2

A reaction product having an acid value of 184 was obtained in a similarmanner to Example 1 except that 306 g of diglycidyl adipate (trade name:"Dinacol EX701", product of Nagase Chemical, Ltd., epoxy equivalent:153) were used in place of "Epicoat 828".

EXAMPLE 3

A reaction product having an acid value of 195 was obtained in a similarmanner to Example 1 except that 252 g of 3,4-epoxycyclohexylmethyl3,4-epoxycyclohexanecarboxylate (trade name: "Chissonox CX221", productof Chisso Corporation) were used instead of "Epicoat 828".

EXAMPLE 4

A reaction product having an acid value of 42.4 was obtained in asimilar manner to Example 1 except that 764 g of "Gafac RE610" (tradename, product of Toho Chemical Industry Co., Ltd.) and 200 g of "Epicoat1001" (trade name, product of Yuka Shell Epoxy Kabushiki Kaisha, epoxyequivalent: 470) were used in lieu of phenylphosphonic acid and "Epicoat828", respectively and the reaction was conducted at 60° C. for 3 hours.

EXAMPLE 5

A reaction product having an acid value of 48.5 was obtained in asimilar manner to Example 4 except that 321.7 g of a monoesterderivative (purity: 95%) of "Gafac RE610" and 200 of "Epicoat 1001" werecharged and the reaction was conducted at 60° C. for 2 hours.

EXAMPLE 6

A reaction product having an acid value of 47.2 was obtained in asimilar manner to Example 4 except that 100 g oftetraglycidylbenzophenone were used instead of "Epicoat 1001" and thereaction was conducted at 60° C. for 2 hours.

EXAMPLE 7

A reaction product having an acid value of 45.0 was obtained in asimilar manner to Example 4 except that the amount of "Gafac RE610" wasreduced from 764 g to 718 g, 144 g of the phenol novolak type "Epicoat154" (trade name, product of Yuka Shell Epoxy Kabushiki Kaisha, epoxyequivalent: 180) were used in lieu of "Epicoat 1001" and the reactionwas conducted at 70° C.

EXAMPLE 8

A reaction product having an acid value of 46.2 was obtained in asimilar manner to Example 4 except that 696 g of "Gafac RS610" (tradename, product of Toho Chemical Industry Co., Ltd.) and 50 g ofdiglycidyl orthophthalate (trade name: "Dinacol EX721", product ofNagase Chemicals, Ltd.) were used in place of "Gafac RE610" and "Epicoat1001", respectively.

EXAMPLE 9

A reaction product having an acid value of 75.8 was obtained in asimilar manner to Example 4 except that 595 g of "Gafac RE410" (tradename, product of Toho Chemical Industry Co., Ltd.) and 75.6 g ofglycerol triglycidyl ester (trade name: "Dinacol EX314", product ofNagase Chemicals, Ltd.) were used in place of "Gafac RE610" and "Epicoat1001", respectively and the reaction was conducted at 50° C. for 2hours.

EXAMPLE 10

A reaction product having an acid value of 71.3 was obtained in asimilar manner to Example 9 except that 102 g of sorbitol polyglycidylether (trade name: "Dinacol EX611", product of Nagase Chemicals, Ltd.)were used in lieu of and "Dinacol EX314" and the reaction was conductedat 50° C. for 3 hours.

EXAMPLE 11

A flask as in Example 1 was charged with 595 g of "Gafac RE410" and 93 gof "Epicoat 828". They were reacted at 100° C. for 30 minutes to obtaina reaction product having an acid value of 72.9.

EXAMPLE 12

A reaction product having an acid value of 50.2 was obtained in asimilar manner to Example 11 except that 718 g of "Gafac RE610" wereused instead of "Gafac RE410", the amount of "Epicoat 828" was reducedfrom 93 g to 74.4 g, and the reaction was conducted at 70° C. for 2hours.

EXAMPLE 13

A flask as in Example 1 was charged with 158.1 g of phenylphosphonicacid and 632 g of tetrahydrofuran, followed by the dropwise addition ofa solution of 74.1 g of glycidol in 296.4 g of tetrahydrofuran at 50° C.over about 2 hours. They were reacted at 50° C. for 1 hour. Afterconfirming the elimination of a spot of glycidol as the raw material bythin layer chromatography on silica gel ("Merck Art 5715", trade name,developer: 1:1 mixed solvent of chloroform and methanol), the solventwas distilled out under reduced pressure from the reaction mixture toobtain a viscous reaction product having an acid value of 280.

EXAMPLE 14

A 1-l separable flask equipped with a thermometer, a stirrer, a nitrogengas inlet tube and a reflux condenser was charged with 100.9 g ofpoly(1,4-butylene adipate) (molecular weight: 1,000), 7.3 g of1,4-butylene glycol, 9.2 g of the reaction product obtained in Example4, 45.0 g of MDI, 270 g of tetrahydrofuran and 270 g of toluene. Afterreacting the at 80-85° C. for 12 hours, 100 g of methyl ethyl ketonewere added to adjust the solid content to 20%.

The resulting phosphoric-acid-modified polyurethane resin had an acidvalue of 2.2 (polymer) and a number average molecular weight of 39,000.

After mixing and kneading 750 g of the phosphoric-acid-modifiedpolyurethane resin solution, 600 g of cobalt-modified γ-Fe₂ O₃ (tradename: "AX-3000", product of Titan Kogyo K.K., specific surface area: 31m² /g), 350 g of cyclohexanone and 650 g of methyl ethyl ketone for 72hours in a ball mill, 20 g of "Desmodule L" were added. The resultantmixture was mixed and kneaded for additional 30 minutes, therebyobtaining a magnetic coating formulation.

A polyester film having a thickness of 9 μm was coated with the magneticcoating formulation to give a coating thickness of 4 μm after drying,followed by drying at 90° C. for 8 hours. The film thus coated was thenslit 4.0 mm wide into magnetic tapes.

EXAMPLE 15

A 1-l separable flask equipped with a thermometer, a stirrer and anitrogen gas inlet tube was charged with 294.6 g of "PTG-1000" (tradename for polyether polyol produced by Hodogaya Chemical Co., Ltd.,molecular weight: 1,000), 16.3 g of 1,4-butylene glycol, 18.9 g ofneopentyl glycol and 24.9 g of the reaction product obtained in Example12. After heating the contents to 80° C., 162.9 g of MDI which had beenheated to 80° C. were added. The resultant mixture was vigorouslystirred for 5 minutes and transferred into a vat, in which the mixturewas allowed to age at 120° C. for 10 hours.

The resultant resin had an acid value of 1.9 and a number averagemolecular weight of 45,000 and was in a solid form. It was dissolved inmethyl ethyl ketone to give a solid content of 20%, thereby providing aresin solution.

Magnetic tapes were then produced in a similar manner to Example 14.

EXAMPLE 16

A flask as in Example 15 was charged with 318.9 g of poly(1,4-butyleneadipate) (molecular weight: 1,000), 23.1 g of 1,4-butylene glycol and15.7 g of the reaction product obtained in Example 5. The contents wereheated to 110° C.

Thereafter, 142.2 g of MDI which had been heated to 110° C. were addedinto the flask, followed by vigorous stirring for 3 minutes. During thestirring, the reaction temperature arose to 220-230° C. because of heatof the reaction. The reaction mixture was transferred into a vat, inwhich it was allowed to age at 60° C. for 10 hours. The resin thusobtained had an acid value of 1.6 and a number average molecular weightof 48,000 and was in a solid form. It was dissolved in methyl ethylketone to give a solid content of 20%, thereby providing a resinsolution.

Magnetic tapes were then produced in a similar manner to Example 14.

EXAMPLE 17

Using 263.5 g of poly(1,4-butylene adipate) (molecular weight: 2,000),22.1 g of 1,4-butylene glycol, 22.7 g of 1,6-hexylene glycol, 31.1 g of"Epicoat 828", 6.2 g of the reaction product obtained in Example 1 and154.4 g of MDI, a solid resin having an acid value of 2.0 and a numberaverage molecular weight of 58,000 was obtained in a similar manner toExample 15. It was dissolved in methyl ethyl ketone to give a solidcontent of 20%, thereby providing a resin solution. Magnetic tapes werethen produced in a similar manner to Example 14.

EXAMPLE 18

A flask as in Example 15 was charged with 297.1 g ofpoly(1,4-cyclohexane dimethanol adipate) (molecular weight: 1,000), 15.0g of 1,6-hexylene glycol, 13.2 g of neopentyl glycol, 25.3 g of "Epicoat1001" and 18.3 g of the reaction product obtained in Example 11. Afterheating the contents to 110° C., 136.9 g of MDI were added and reactedunder similar conditions to Example 16.

The reaction mixture was transferred into a vat and was then allowed tocool down. Thereafter, it was allowed to age at 60° C. for 10 hours. Theresin thus obtained had an acid value of 1.8 and a number averagemolecular weight of 52,000 and was in a solid form. It was dissolved inmethyl ethyl ketone to give a solid content of 20%, thereby providing aresin solution.

Magnetic tapes were then produced in a similar manner to Example 14.

EXAMPLE 19

A flask as in Example 15 was charged at 70° C. with 261.4 g ofpoly(1,4-butylene adipate) (molecular weight: 2,000), 25.9 g of1,6-hexylene glycol, 22.8 g of neopentyl glycol, 32.4 g of diethyleneglycol diglycidyl ether (trade name: "YED 205", product of Yuka ShellEpoxy Kabushiki Kaisha, aliphatic epoxy compound, epoxy equivalent: 140)and 10.1 g of "Gafac RE-410" (phosphoric acid ester produced by TohoChemical Industry Co., Ltd.). The contents were heated to 110° C. overabout 10 minutes.

Thereafter, under similar conditions to Example 16, 147.4 g of MDI wereadded and reacted and the reaction mixture was allowed to age.

The resin thus obtained had an acid value of 1.8 and a number averagemolecular weight of 47,000 and was in a solid form. It was dissolved inmethyl ethyl ketone to give a solid content of 20%, thereby providing aresin solution.

Magnetic tapes were then produced in a similar manner to Example 14.

EXAMPLE 20

A flask as in Example 14 was charged with 640 g of methyl ethyl ketone,100.5 g of poly(1,4-butylene adipate) (molecular weight: 1,000), 8.4 gof neopentyl glycol, 0.8 g of "Epicoat 828" and 3.2 g of "Gafac RE410".They were reacted at 78° C. for 3 hours. MDI (47.1 g) was added further,followed by a reaction at 78° C. for 15 hours. The resultant resinsolution had a solid content of 20%. The polymer had an acid value of1.9 and a number average molecular weight of 45,000.

Magnetic tapes were then produced in a similar manner to Example 14.

EXAMPLE 21

A flask as in Example 15 was charged at 70° C. with 290.6 g ofpolycarbonate polyol (product of Toagosei Chemical Industry Co., Ltd.),16.1 g of 1,4-butylene glycol, 18.6 g of 1,6-hexylene glycol, 2.5 g of"Epicoat 828" and 11.3 g of "Gafac RS-410" (product of Toho ChemicalIndustry Co., Ltd.). After heating the contents to 110° C. over 10minutes, the reaction mixture was allowed to age at 110° C. for 10minutes.

Similarly to Example 16, 160.8 g of MDI were then added and reacted andthe reaction mixture was allowed to age.

The resultant resin had an acid value of 2.0 and a number averagemolecular weight of 45,000 and was in a solid form. It was dissolved inmethyl ethyl ketone to give a solid content of 20%, thereby providing aresin solution.

Magnetic tapes were then produced in a similar manner to Example 14.

EXAMPLE 22

In a similar manner to Example 14, a phosphoric-acid-modifiedpolyurethane resin solution was prepared. It was neutralized withcaustic potash in an amount equivalent to the acid value.

The solution was diluted with methyl ethyl ketone to give a solidcontent of 20%. Magnetic tapes were then produced in a similar manner toExample 14.

EXAMPLE 23

Using 281.1 g of poly(1,4-butylene adipate) (molecular weight: 1,000),12.2 g of 1,4-butylene glycol, 21.2 g of neopentyl glycol, 29.2 g of thereaction product obtained in Example 11 and 156.2 g of MDI, a solidresin having an acid value of 5.5 and a number average molecular weightof 45,000 was obtained in a similar manner to Example 16.

Magnetic tapes were then produced in a similar manner to Example 14.

EXAMPLE 24

A flask as in Example 14 was charged with 94.6 g of poly(1,4-butyleneadipate) (molecular weight: 1,000), 8.0 g of 1,4-butylene glycol, 1.1 gof the reaction product obtained in Example 13, 103.7 g of MDI and 225 gof tetrahydrofuran. After reacting them at 65° C. for 10 hours, 375 g oftetrahydrofuran were added to give a solid content of 20%.

The resultant phosphoric-acid-modified polyurethane resin had an acidvalue of 1.8 (polymer) and a number average molecular weight of 52,000.

Magnetic tapes were then produced in a similar manner to Example 14.

EXAMPLE 25

A flask as in Example 15 was charged with 226.1 g of poly(1,4-butyleneadipate) (molecular weight: 1,000), 60.7 g of neopentyl glycol and 7.1 gof the reaction product obtained in Example 13. The contents were thenheated to 110° C.

Under similar conditions to Example 16, 206 g of MDI were then added andreacted and the reaction mixture was allowed to age.

The thus-obtained resin had an acid value of 3.1 and a number averagemolecular weight of 62,000 and was in a solid form. It was dissolved inmethyl ethyl ketone to give a solid content of 20%, thereby providing aresin solution.

Magnetic tapes were then produced in a similar manner to Example 14.

EXAMPLE 26

A flask as in Example 15 was charged with 226.1 g of poly(1,4-butyleneadipate) (molecular weight: 1,000), 60.7 g of neopentyl glycol, 7.1 g ofthe reaction product obtained in Example 13 and 5.7 g oftri-n-butylamine. The contents were then heated to

Under similar conditions to Example 16, 206 g of MDI were then added andreacted and the reaction mixture was allowed to age.

The thus-obtained resin had an acid value of 3.0 and a number averagemolecular weight of 59,500 and was in a solid form. It was dissolved inmethyl ethyl ketone to give a solid content of 20%, thereby providing aresin solution.

Magnetic tapes were then produced in a similar manner to Example 14.

EXAMPLE 27

In a similar manner to Example 25, a phosphoric-acid-modifiedpolyurethane resin solution was prepared. It was neutralized withtriethylamine in an amount equivalent to the acid value. The solutionwas diluted with methyl ethyl ketone to give a solid content of 20%.

Magnetic tapes were then produced in a similar manner to Example 14.

COMPARATIVE EXAMPLE 1

"Estan-®5701Fl" (trade name, product of The B.F. Goodrich Company) wasdissolved in a 70:30 mixture of tetrahydrofuran and cyclohexanone togive a solid content of 20%.

Using 750 g of the resin solution, 600 g of cobalt-modified Y-Fe203("A-3000" trade name; product of Titan Kogyo K.K.), 650 g ofcyclohexanone and 350 g of methyl ethyl ketone, magnetic tapes were thenproduced in a similar manner to Example 14.

COMPARATIVE EXAMPLE 2

5703"(product of The B.F. Goodrich Company) was dissolved in methylethyl ketone to give a solid content of 20%.

Magnetic tapes were then produced in a similar manner to Example 14.

COMPARATIVE EXAMPLE 3

A 1-l separable flask equipped with a thermometer, a stirrer and anitrogen gas inlet tube was charged with 325.4 g of poly(1,4-butyleneadipate) (molecular weight: 1,000), 23.4 g of 1,4-butylene glycol and6.1 g of "Epicoat 1001". After heating the contents to 80° C., 145.1 gof MDI which had been heated to 80° C. were added and the resultantmixture was vigorously stirred. Thereafter, the reaction mixture wastransferred into a vat, in which it was allowed to age at 120° C. for 10hours. A solid resin having a number average molecular weight of 44,000was obtained.

Magnetic tapes were then produced in a similar manner to Example 14.

COMPARATIVE EXAMPLE 4

A flask as in Example 14 was charged with 118.4 g of poly(1,4-butyleneadipate) (molecular weight: 1,000), 2.1 g of 1,4-butylene glycol, 1.4 gof 2,2-dimethylolpropionic acid, 38.1 g of MDI, 270 g of tetrahydrofuranand 270 g of toluene. After reacting them at 80-85° C. for 12 hours, 100g of tetrahydrofuran were added to give a solid content of 20%.

The resultant carboxyl-modified polyurethane resin had an acid value of3.5 and a number average molecular weight of 52,000.

Magnetic tapes were then produced in a similar manner to Example 14.

COMPARATIVE EXAMPLE 5

A flask as in Example 14 was charged with 116.6 g of poly(1,4-butyleneadipate) (molecular weight: 1,000), 2.5 g of 1,4-butylene glycol, 2.8 gof 5-sodiumsulfo-1,3-di(2-hydroxyethyl) isophthalate (product ofSumitomo Chemical Co., Ltd.), 38.1 g of MDI, 270 g of tetrahydrofuranand 270 g of toluene. After reacting them at 80-85° C. for 12 hours, 100g of methyl ethyl ketone were added to give a solid content of 20%.

The resultant sodium sulfonate-modified polyurethane resin had a sodiumsulfonate (--SO₃ Na) concentration of 0.05 mg eq/g and a number averagemolecular weight of 48,000.

Magnetic tapes were then produced in a similar manner to Example 14.

COMPARATIVE EXAMPLE 6

A flask as in Example 14 was charged with 468 g of dimethylformamide and115 g of a hydroxyl-terminated polyurethane 5703", trade name; productof The B.F. Goodrich Company). After dissolving the latter in the formerat 80° C. over 2 hours, 8.2 g of the compound represented by thefollowing formula: ##STR3## and 1.6 g of pyridine were added. Adehydrochlorination reaction was then conducted at 80° C. for 3 hours,whereby phosphoric acid groups were introduced into both ends of eachpolyurethane chain, respectively. Subsequent to neutralization withcaustic soda, the polymer was poured into a large volume of methanol.Further, the polymer was washed several times with methanol.

After drying the polymer under reduced pressure, methyl ethyl ketone wasadded to adjust the solid content to 20%.

The sodium-phosphate-modified polyurethane resin thus obtained had asodium phosphate residuum ##STR4## concentration of 1.8 mg eq/g and anumber average molecular weight of 58,000.

Magnetic tapes were then produced in a similar manner to Example 14.

With respect to each of the magnetic tapes obtained in the aboveexamples and comparative examples, its surface gloss (60° reflectivity)and square ratio (Br/Bs) were measured to investigate the dispersion andmagnetic characteristics, respectively. In addition, its abrasionresistance was also measured to investigate the durability. The resultsare summarized in Table 1.

The above properties were measured in accordance with the followingtesting methods, respectively.

SURFACE GLOSS

The surface gloss (60° reflectivity) of the magnetic coating layer ofeach magnetic tape was measured using a gloss meter ("AU-SCH-2D-GU3",trade name for a digitized automatic colorimetric color difference metermanufactured by Toho Rika Kogyo K.K.).

Better dispersion gives a higher gloss value.

SQUARE RATIO

Measurement was conducted using "Model 3257", trade name for anautomatic recording apparatus for d.c. magnetization characteristicsmanufactured by Yokogawa Electric Corporation.

Better dispersion gives a higher square ratio.

ABRASION RESISTANCE

A crock testing machine of the JSPSR (Japan Society for Promotion ofScientific Research) type manufactured by Daiei Kagaku Seiki SeisakushoK.K. was used. In an environment of 23° C. and 65% RH, the surface ofthe magnetic coating layer of each magnetic tape was reciprocated andrubbed 200 times under a load of 100 g against a chromium-plated metalcylinder having a diameter of 15 mm. Then, the percentage of anyrubbed-off surface area was determined based on the total surface areasubjected to the rubbing.

                  TABLE 1                                                         ______________________________________                                                 Surface   Square  Abrasion                                                    gloss, %  ratio   resistance, %                                      ______________________________________                                        Example 14 88          0.84    3.5                                            Example 15 93          0.83    4.0                                            Example 16 92          0.84    1.9                                            Example 17 90          0.81    1.6                                            Example 18 85          0.82    1.3                                            Example 19 74          0.78    2.1                                            Example 20 70          0.75    5.0                                            Example 21 80          0.80    4.7                                            Example 22 90          0.82    3.4                                            Example 23 95          0.85    3.2                                            Example 24 92          0.83    2.5                                            Example 25 93          0.82    3.6                                            Example 26 96          0.85    3.3                                            Example 27 98          0.86    3.4                                            Comp. Ex. 1                                                                              16          0.68    1.5                                            Comp. Ex. 2                                                                              20          0.72    3.2                                            Comp. Ex. 3                                                                              17          0.65    2.4                                            Comp. Ex. 4                                                                              50          0.74    3.5                                            Comp. Ex. 5                                                                              68          0.76    8.0                                            Comp. Ex. 6                                                                              52          0.74    5.2                                            ______________________________________                                    

It is clearly envisaged from Table 1 that the magnetic tapes accordingto the present invention, namely, those of Examples 14-27 are allexcellent in dispersion and especially the magnetic tapes of Examples16-18 in which phosphoric-acid-modified and epoxy-modified polyurethaneresins were used respectively are also excellent in durability.

We claim:
 1. A magnetic recording medium comprising a magnetic layercomposed principallyof magnetic particles and a binder, characterized inthat at least a portion of the binder is a polyurethane resinsynthesized from a reactant mixture of components (1), (2), (3) and (4)set out below, containing one phosphoric acid group or one residualgroup derived from phosphoric acid per 3,000-200,000 number averagemolecular weight of the polyurethane resin, and having a number averagemolecular weight of 4,000-150,000:(1) a phosphorus compound (a)represented by a structural formula set out below or a phosphoruscompound (b) represented by a structural formula set out below: ##STR5##wherein R¹ is a hydrogen atom, a phenyl group, an aklyl group having1-40 carbon atoms, or an alkylphenyl group having 1-40 carbon atoms, andn is an integer of 0-30; ##STR6## wherein R² is a phenyl group, an alkylgroup having 1-40 carbon atoms, or an alkylphenyl group having 1-40carbon atoms; (2) an epoxy compound having at least two epoxy groupsand/or an epoxy compound having one epoxy roupand at least one hydroxylgroup; (3) a bifunctional isocyanate compound and/or a trifunctionalisocyanate compound; and (4) a polyfunctional hydroxy compound having anumber average molecular weight of 400-5,000.
 2. The magnetic recordingmedium according to claim 1, wherein the reactant mixture furthercomprises a component (5) a chain extender.
 3. The magnetic recordingmedium according to claim 1, wherein phosphoric acid groups or residualgroups derived from phosphoric acid, said groups being contained in thepolyurethane resin, have been at least partly neutralized with a base.4. The magnetic recording medium according to claim 2, whereinphosphoric acid groups or residual groups derived from phosphoric acid,said groups being contained in the polyurethane resin, have been atleast partly neutralized with a base.